Until recently, only a slight majority of Democrats correctly believed that the ACA increased the number of insured people in America. You are vastly underestimating the public's ability to be ill-informed and fall victim to disinformation where attribution is concerned.
So you're saying many Democrats didn't know the full extent of the ACA's success, therefore the millions of people thrown off their insurance because of the ACHA won't blame Trump? That's two very different levels of ignorance. Anyway, why would they attribute a solid economy to Trump (which you said they'd do) but then attribute their inability to get healthcare to something/someone else?
Trump got it together for the final days of the election in terms of stopping tweeting horrific things. You have to remember that the public's political memory is very shallow and very short.
Depending on what it is. Hillary lost in no small part to stupid crap that had been said about her for literally decades. People will remember what they want to. I just don't see millions of Americans losing their healthcare and then saying, "No worries, I never expected Trump to keep his promise." Trump oversold his plan, and there is no way it can possibly live up to expectations. That reality will crash down at some point, and sooner the better.
If his handlers are able to persuade him to knock it off a few months before the 2018 election and economic numbers remain good, you probably will see his approval numbers strengthen considerably.
Trump doesn't listen to his handlers and I really don't know what evidence exists to suggest otherwise. He does what he wants to do and when he wants to do it, common sense and etiquette be damned. But no doubt his numbers will creep up eventually. I wasn't saying they'd stay below 40 throughout his entire Presidency.